Diazocyano acids have been used as an initiator for polymerization such as homopolymerization of acrylamide or 1,3-butadiene or copolymerization of 1,3-butadiene with acrylonitrile (see e.g., U.S. Pat. No. 3,285,949).
As means for the preparation of diazocyano acids, there is known a process comprising reacting a keto acid or its sodium salt with a cyanogen compound such as sodium cyanide or hydrogen cyanide and a hydrazine such as hydrazine hydrate or hydrazine sulfate in water to form a hydrazo compound, adding chlorine gas to the obtained solution to oxidize the hydrazo compound and form a diazocyano acid and filtering off the solid diazocyano acid from the obtained reaction mixture (see U.S. Pat. No. 3,285,949).
However, this known process has the following problems:
(a) Since sodium chloride is formed as a by-product in an amount of at least 2 moles per mole of a diazocyano acid when the diazocyano acid is synthesized, a large amount of sodium chloride is contained in the diazocyano acid product. A diazocyano acid containing a large amount of sodium chloride is not preferred as the initiator for homopolymerization of 1,3-butadiene or copolymerization of 1,3-butadiene with acrylonitrile. Diazocyano acids containing too much sodium chloride will cause a clarity problem when cured with epoxy resins; additionally, the sodium chloride is not desirable when insulating properties from the polymers are needed.
(b) If a refining step is arranged for removing sodium chloride contained in the diazocyano acid, the yield of the diazocyano acid is drastically reduced.
U.S. Pat. No. 4,684,717 (Ashitaka et al, Aug.4, 1987) provides a process for the preparation of diazocyano acid, which comprises reacting a keto acid or its sodium salt with a cyanogen compound such as sodium cyanide or hydrogen cyanide and a hydrazine in water to form a concentrated aqueous solution of a hydrazo compound, adding acetone or acetone and water to the concentrated aqueous solution to form an acetone water solution of the hydrazo compound. An oxidant, such as chlorine gas is added to the solution to oxidize the hydrazo compound and form a diazocyano acid. Transparent liquid layers are formed by adding acetone and/or water to the obtained reaction mixture during or after oxidation if necessary. Sodium chloride is added to the reactive mixture, if necessary, and separated and recovered in the uppermost layer of the acetone-water solution containing the diazocyano acid.
U.S. Pat. No. 4,684,718 (Ashitaka et al, Aug. 4, 1987) provides a process for the preparation of diazocyano acid, which comprises reacting a keto acid or its sodium salt with a cyanogen compound such as sodium cyanide or hydrogen cyanide and a hydrazine in water to form a concentrated aqueous solution of a hydrazo compound, adding acetone or acetone and water to the concentrated aqueous solution to form a solution of the hydrazo compound. Chlorine gas is added to the solution to oxidize the hydrazo compound and form a diazocyano acid which is separated out from the obtained reaction mixture.